Tribological behavior of ZnO-Si₃N₄ nanoparticles-based lubricating grease

Figures & data

Figure 1. XRD spectrogram of (a) ZnO and (b) Si₃N₄.

Figure 2. TEM images of ZnO (A) nanoparticles and Si₃N₄ (B) nanoparticles.

Table 1. Physical and chemical parameters of lithium grease.

Property	Lithium grease
Density (20 °C) (kg/m^3)	950
NIGI grade	3
Unworked penetration (1/10 mm at 25 °C)	280
Dropping point (°C)	≥180
Water spray loss (38 °C, 1h, %)	1.65

Table 2. ZnO nanoparticles content.

No.	A1	A2	A3	A4	A5	A6
Base grease (wt%)	100%	99.5%	99.0%	98.8%	98.7%	98.6%
ZnO (wt%)	0	0.5%	1.0%	1.2%	1.3%	1.4%

Table 3. Si₃N₄ nanoparticles content.

No.	B1	B2	B3	B4	B5	B6
Base grease (wt%)	100%	99.9%	99.8%	99.7%	99.6%	99.5%
Si3N4 (wt%)	0	0.1%	0.2%	0.3%	0.4%	0.5%

Table 4. Mixed nanoparticles content.

No.	C1	C2	C3	C4	C5	C6
ZnO (wt%)	0	0.8%	0.9%	1.0%	1.1%	1.2%
Si3N4 (wt%)	0	0.7%	0.6%	0.5%	0.4%	0.2%

Table 5. Mixed nanoparticles content.

No.	D01	D02	D03
samples	ZnO	Si3N4	composite nanoparticles

Figure 3. Principle diagram of four-ball friction.

Figure 4. Schematic diagram of testing apparatus.

Figure 5. Overall view of test machine.

Figure 6. (a) Friction coefficient vs time at different ZnO contents; (b) Wear scar diameter of steel balls at different ZnO contents.

Figure 7. (a) Friction coefficient vs time at different Si₃N₄ contents; (b) Wear scar diameter of steel balls at different Si₃N₄ contents.

Figure 8. (a) Friction coefficient vs time at different ZnO-Si₃N₄ contents; (b) Wear scar diameter of steel balls at different ZnO-Si₃N₄ contents.

Figure 9. Average reduction (%) of friction coefficient and wear scar diameter of lubricating greases with single and composite nanoparticles.

Figure 10. Wear scar morphology of (a), (c), (e) base grease and (b), (d), (f) composite nanoparticles-based grease.

Figure 11. (a) SEM images of wear surface by using base grease and (b) composite nanoparticles-based grease.

Figure 12. (a) Morphology and (b) original wave crest curve of wear surface by using composite nanoparticles-based grease.

Table 6. Surface element distribution.

Element	O	Si	P	S	Ca	Cr	Fe	Zn
Weight percent	5.74	0.44	2.46	4.63	0.56	1.02	82.19	2.96
Atomic percent	16.71	0.73	3.69	6.72	0.65	0.92	68.48	2.11

Figure 13. Bearing temperature-rotating speed curve.

Figure 14. Vibration acceleration-rotating speed curve.

Figure 15. Noise-rotating speed curve.